1. Field of the Invention
This invention relates generally to antenna systems, and more particularly to vehicle-mounted antennas for use with warehouse management systems.
2. Description of Related Art
Current “best practices” employed in the movement and tracking of goods in warehouses and distribution centers include the use of barcode-based data collection and wireless networked computers on lift trucks and other mobile material handling equipment. While these technologies have greatly enhanced the efficiency and accuracy of warehousing operations over recent decades, they still fundamentally rely on manual data collection activity in the validation of material movement. Two aspects are key elements to enhance efficiency.
One aspect is automated data collection needs to be synchronized with operator directives and activity. Operators are typically presented with instructions from the warehouse management software application on the screen of a mobile wireless computer on the lift truck. Upon completion of the required action, the operator typically enters data through a bar code scan or keyboard entry to confirm accurate completion of the task. The information is transmitted over a wireless connection to the application on a network server. The application may then assign the operator the next task. Thus, the application and process require real-time, precise data, appropriate to the task and synchronous with operator actions and application instructions.
The second aspect is that almost all full pallet load moves require two basic data collection elements: (1) load identification and (2) location identification. If, for instance, a lift operator is instructed to drive to a particular location, he may then be required to scan a bar code to verify that he has arrived at the correct location. If he is then directed to pick up a pallet, he may then be required to scan a bar code on the pallet load to identify the load to the application software. A subsequent instruction to deposit the load at a particular location would typically be followed by a bar code scan identifying the deposit location to validate task compliance. Each of these scanning activities requires human intervention or other additional activity that can reduce overall process efficiency. Thus, these processes can be improved if the above data collection elements could be more seamlessly integrated into existing warehouse activities.
The use of radio frequency identification (RFID) technology presents great promise for automating the data collection process. A RFID system typically uses a RFID tag reader to query a RFID tag attached to an object. The RFID tag provides certain information associated with the tagged object.
Prior attempts to effectively implement RFID technology in a warehouse environment have typically failed to fully take into account the aspects mentioned above. For example, the use of RFID “portals” at dock doors in warehouses is typically intended to deliver identification of the load passing through the portal and to designate the location (dock door) identification through the reader's network address. However, this is seldom synchronized with lift operator instructions and application instructions to the operator. Also, the attractive characteristic of RFID as a solution approach is that it can be automated easily and does not require “line of sight” to identify items or locations. RFID systems can, and typically do, read multiple tags; but this often results in extraneous data, which fails to deliver discrete, precise data as required by the application. Thus, the use of RFID systems in warehouse inventory control presents a unique set of problems that have to be resolved to ensure efficient operation of the RFID system.
To be successful for use in a warehouse inventory control, the RFID-based solution should address the first and second aspects above. A key to the first aspect will be that the RFID implementation becomes inherently part of the synchronized activities of the lift operation itself. A key to the second aspect will be that the RFID implementation collects precisely the data expected and required at each step of the lift operation.
With specific reference to warehouse inventory control, the RFID system has to efficiently operate in a harsh operating environment that is typical of a warehouse. RFID tag readers are installed at various locations in the warehouse. Some of these locations are stationary mounting locations, such as that of a RFID tag reader installed on a post located adjacent to a conveyor belt. Other locations are mobile mounting locations, such as that of a RFID tag reader installed on a forklift. One particular function of the RFID tag reader mounted on the forklift is to communicate with RFID tags attached to various objects transported by the forklift.
Mounting the RFID tag reader upon the forklift involves several operational as well as logistical considerations. Consequently, prior to installation of the RFID tag reader, an acceptable mounting location has to be identified such that installation and operation of the RFID tag reader will not interfere with, nor be affected by, the operation of the forklift. Particularly, antennas for communicating with RFID tags should be mounted in a manner that addresses multiple factors.
For example, in some instances, a limited signal strength is required to prevent reading of undesired adjacent RFID tags. Thus, there may be a need to mount antennas for the RFID reader at the front area of the forklift. Furthermore, signal strength requirements may vary for particular applications or types of inventory packaging. Antennas should be located in a manner to improve probability of a correct tag read for numerous inventory types and power requirements.
Another factor is the rugged environment of warehouse operations and mobile material handling equipment. An antenna must have either an adequate structure or secured location to withstand this rugged environment. However, the ruggedized antenna structure should still accommodate typical forklift operations and of standard-size pallets. In some applications it may be preferable to retrofit existing forklift equipment with RFID capable equipment or to provide other cost-effective means of incorporating RFID.
RFID tag alignment can present another factor. When RFID tags are improperly aligned or partially obscured, an interrogating antenna may not be able to read the RFID tag. Thus, to improve tag read rates, there may be a need for multiple antennas to project signals from different positions relative to tags on the pallet. Depending on the interrogating antenna and tag locations, improved read rates may also be possible through the use of particularly polarized signal patterns. In some environments forklifts incorporate double-length (or longer) tines for carrying two (or more) sets of pallets. It would be desirable to automatically and effectively read both sets of pallets and to distinguish between the two sets.
Today, commercial RFID technology operates at ultra-high frequencies (UHF) or microwave frequencies using backscatter coupling techniques. Antenna systems that can support these frequencies, while meeting the above needs are required.